Open a saved carrier, or pick a new one from the main-system API (it must already exist there — Status, BillingMode, and upload need that record). Choose or name a file format, load columns, then Save. Import files may use a different spelling; you still cannot invent a carrier that is not in the API. Import tab lists saved carriers only.
2. Import file
Import file should be CSV format.
3. Problem rows
Loads automatically after Process, when you open Advanced, or when you click Needs fixing on a past run. After Setup (carrier values → standard codes) and Save Carrier, use Retry Import.